Silicon Self-Diffusion Using Isotopically Enriched ^<28>Si Epitaxial Layers

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In Si LSI process such as oxidation, ion implantation and so on, point defects (vacancy and Si self-interstitial) exist in non-thermal state. With the shirink of device dimension, control of these processes becomes more and more important. Generally, the behavior of point defects in semiconductor can be investigated by self-diffusion. However, it is very difficult to perform the experiment on self-diffusion in Si because of its very short half life. In this work, we determined Si self diffusion coefficient using isotopically enriched ^<30>SiH_4 gas source and clarified the role of point defects in Si self-diffusion. Main results of the work are as follows. (i) We succeeded to grow the isotopically pure ^<30>Si epitaxial layers for the first time. (ii) Using the hetero-structures of ^<30>Si/ natural Si, Si self diffusion coefficient was determined at temperatures of 850-1050℃ by estimating the ^<30>Si concentration profiles in natural Si with SIMS.(iii) Doping dependence on Si self diffusion (Fermi level effect) was investigated and clarified the role of point defect on Si self diffusion. Three different Si substrates (heavily As doped Si=3x10^<19>cm^<-3>, heavijy B doped Si=2x10^<19>cm^<-3>, and B doped Si=1x10^<16>cm^<-3>) were prepared. Si self-diffusion coefficient in extrinsic p-type Si is twice larger than that of intrinsic Si, while self diffusion coefficient in extrinsic n-type Si is almost same as that of intrinsic Si. In extrinsic n-type Si, excess vacancies exist due to the Fermi level effect. However the present results indicate that the role of vacancy on Si self-diffusion is very small at lower temperatures (850, 900℃) because of little influence of heavily n-type doping on self-diffusion coefficient. It clarifies that the general opinion-vacancy is dominant in Si self-diffusion at lower temperature region-cannot hold.